1. Field of the Invention
This invention relates to a composition made up of a specific visible light-curing agent and a polyester resin. More particularly, this invention relates to a visible light-curing polyester resin composition which enjoys a long pot life in a dark place, cures quickly, and to a visible light-curing polyester composition from which there can be cured to form a shaped product which exhibits only slight difference in rigidity between its obverse and reverse sides
2. Prior Art Statement
It has been known that a radically polymerizable unsaturated polyester resin can be cured when it is admixed with a photocuring agent and then exposed to ultraviolet radiation (UV) or visible light. Particularly for the purpose of curing a thin film of resin to be used as a surface coating or ink, a method which specifically makes use of the UV has been established. When the resin is used in the form of a thickly applied layer reinforced with glass fibers, however, the exposure to the UV radiation is not appropriate for curing the resin because the resin itself or the reinforcing glass fibers prevent the radiation from being absorbed enough for thorough curing of the resin. It has been also known that visible light is effective for curing a resin used in the form of a thickly applied layer or reinforced with glass fibers.
Various curing systems of unsaturated polyester resin settable by the visible light have been reported. In the specification of Japanese Patent Publication SHO 60(1985)-15646, for example, a combination of a benzoyloxime carbonate ester derivative with a photoreducing dye such as, for example, eosine, and a tertiary amine as a photocuring agent is proposed. In the specifications of Japanese Patent Publication SHO 54(1979)-10986, SHO 57(1982)-59246, and SHO 60(1985)-8241, combinations of .alpha.-diketones with tertiary amines are disclosed. An example using acylophosphine oxide as a photocuring agent is disclosed in the specification of Japanese Patent Publication SHO 60(1985)-8047. Besides, a method which resorts to additional use of a peroxide as a photocuring agent has been known to the art. In the specification of Japanese Patent Publication SHO 57(1982)-202304, for example, a combination using benzophenone or benzil and t-butylperoxybenzoate, methylethyl ketone peroxide, or cyclohexanone peroxide as a peroxide is disclosed as a photocuring agent.
The known methods described above, however, suffer from the drawbacks described below.
The polyester resin composition containing as a curing agent the combination of a benzoyloxime carbonate ester derivative, a photoreducing dye, and a tertiary amine does not cure quickly and the shaped article obtained by curing the composition has low rigidity. The reverse side of the shaped product obtained by curing the polyester resin composition containing as a curing agent the combination of an .alpha.-diketone and a tertiary amine or an acylophosphine oxide has low rigidity.
The polyester resin composition which contains the photocuring agent additionally using a peroxide has no problem regarding the rigidity of the reverse side of the shaped article. It nevertheless has the disadvantage that the pot life thereof is only about one week.
As described above, none of the conventional visible light-curing agents is known to possess such a quality that the resin incorporating the agent enjoys a long pot life and the shaped article obtained by curing the resin molded in a given shape exhibits physical properties, particularly rigidity, substantially uniformly throughout the entire mass thereof, specifically with sparing difference between the obverse side and the reverse side. One major use of polyester resins is for FRP. The fact that the rigidity of a shaped article differs on the obverse side and the reverse side thereof makes polyester resin practically unfit for the FRP.